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res_pjsip_t38.c: Fix deadlock in T.38 framehook.

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A deadlock can happen between a channel lock and a pjsip session media
container lock.  One thread is processing a reINVITE's SDP and walking
through the session's media container when it waits for the channel lock
to put the determined format capabilities onto the channel.  The other
thread is writing a frame to the channel and processing the T.38 frame
hook.  The T.38 frame hook then waits for the pjsip session's media
container lock.  The two threads are now deadlocked.

* Made the T.38 frame hook release the channel lock before searching the
session's media container.  This fix has been done to several other
frame hooks to fix deadlocks.

ASTERISK-26974 #close

Change-Id: Ie984a76ce00bef6ec9aa239010e51e8dd74c8186
This commit is contained in:
Richard Mudgett
2017-04-29 16:11:21 -05:00
parent bf7cf10d15
commit 9d5df48968
1 changed files with 20 additions and 10 deletions
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30
res/res_pjsip_t38.c
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@@ -400,7 +400,8 @@ static int t38_interpret_parameters(void *obj)
}
/*! \brief Frame hook callback for writing */
static struct ast_frame *t38_framehook_write(struct ast_sip_session *session, struct ast_frame *f)
static struct ast_frame *t38_framehook_write(struct ast_channel *chan,
struct ast_sip_session *session, struct ast_frame *f)
{
if (f->frametype == AST_FRAME_CONTROL && f->subclass.integer == AST_CONTROL_T38_PARAMETERS &&
session->endpoint->media.t38.enabled) {
@@ -414,27 +415,36 @@ static struct ast_frame *t38_framehook_write(struct ast_sip_session *session, st
ao2_ref(data, -1);
}
} else if (f->frametype == AST_FRAME_MODEM) {
RAII_VAR(struct ast_sip_session_media *, session_media, NULL, ao2_cleanup);
struct ast_sip_session_media *session_media;
if ((session_media = ao2_find(session->media, "image", OBJ_KEY)) &&
session_media->udptl) {
/* Avoid deadlock between chan and the session->media container lock */
ast_channel_unlock(chan);
session_media = ao2_find(session->media, "image", OBJ_SEARCH_KEY);
ast_channel_lock(chan);
if (session_media && session_media->udptl) {
ast_udptl_write(session_media->udptl, f);
}
ao2_cleanup(session_media);
}
return f;
}
/*! \brief Frame hook callback for reading */
static struct ast_frame *t38_framehook_read(struct ast_sip_session *session, struct ast_frame *f)
static struct ast_frame *t38_framehook_read(struct ast_channel *chan,
struct ast_sip_session *session, struct ast_frame *f)
{
if (ast_channel_fdno(session->channel) == 5) {
RAII_VAR(struct ast_sip_session_media *, session_media, NULL, ao2_cleanup);
struct ast_sip_session_media *session_media;
if ((session_media = ao2_find(session->media, "image", OBJ_KEY)) &&
session_media->udptl) {
/* Avoid deadlock between chan and the session->media container lock */
ast_channel_unlock(chan);
session_media = ao2_find(session->media, "image", OBJ_SEARCH_KEY);
ast_channel_lock(chan);
if (session_media && session_media->udptl) {
f = ast_udptl_read(session_media->udptl);
}
ao2_cleanup(session_media);
}
return f;
@@ -447,9 +457,9 @@ static struct ast_frame *t38_framehook(struct ast_channel *chan, struct ast_fram
struct ast_sip_channel_pvt *channel = ast_channel_tech_pvt(chan);
if (event == AST_FRAMEHOOK_EVENT_READ) {
f = t38_framehook_read(channel->session, f);
f = t38_framehook_read(chan, channel->session, f);
} else if (event == AST_FRAMEHOOK_EVENT_WRITE) {
f = t38_framehook_write(channel->session, f);
f = t38_framehook_write(chan, channel->session, f);
}
return f;